216 TRAXSACTIO^-S LIVERPOOL BIOLOGICAL SOCIETY. 



Pseudocahmus elongatus and Oithona similis!, usually 

 reg-arded as oceanic, are present in quantity in Port Erin 

 Bay all the year round. Again Temora longicornis, a 

 reputed neritic species, is at Port Erin a summer form 

 only abundant in June and July — a distribution wliicL 

 might be supposed to be characteristic of the immigration 

 of an oceanic species. It must be remembered, however, 

 that periodicity, and absence or great reduction in 

 numbers during part of the year may be due to the normal 

 life-history of a neritic species //; situ and need not 

 indicate invasion from outside. 



The fresh evidence this year tends merely to confirm 

 us in the opinion expressed in last year's report*, to the 

 effect that — " It is improbable that all planktonic species 

 are either oceanic or neritic. It may well be that some 

 species are intermediate in character and habitat, over- 

 lapping and intermingling with both, and liable to be 

 placed sometimes in the one category and sometimes in 

 the other. Then again, there may be some species which 

 are cosmopolitan, or ' Panthalassic,' as we should prefer 

 to call it, occurring both in the open oceans and also in 

 the shallower coastal waters of some parts of the world." 



Cladocera. 



This summer group ranged in 1911 from March 2nd 

 to September 29th. radon (with 3,500), and Evadne 

 (with 6,460), both reached their highest ])oint early in 

 September; but Podon also showed large hauls in June 

 (1,320) and August (1,350), and Evadne in June (6,000), 

 July (2,400), and August (2,550). These numbers, it will 

 be noticed, are distinctly larger than those for 1910. 



* Lancashire Sea Fisheries Laboratory Report for 1910, p. 107. 



